New thioether- and thianthrene-containing poly(benzoxazole)s (PBOs) were synthesized from 4,4’-thiobis[3-chlorobenzoic acid] and thianthrene-2,7- and -2,8-dicarbonyl chlorides with commercially available bis-o-aminophenols. Polymers were prepared via solution polycondensation in poly(phosphoric acid) at 90-200 degrees C. Transparent PBO films were cast directly from polymerization mixtures or m-cresol. The films were flexible and tough. Nonfluorinated PBOs were soluble only in strong acids and AlCl3/NO(2)R systems by forming complexes with the benzoxazole heterocycle. Glass transition temperatures ranged from 298-450 degrees C, and thermogravimetric analysis showed good thermal stabilities in both air and nitrogen atmospheres.